Communication systems in high speed systems such as, for example, Ethernet systems, generally include a transmitter that provides signals to a receiver over a communication channel. Often, the communication channel is a low pass channel such as, for example, a copper wire, a copper trace on a printed circuit board, an optical fiber, etc. Generally, since the communication channel is usually a low pass channel, high frequencies of the signals are attenuated over the communication channel. Accordingly, the receiver generally includes a pre-filter, and more particularly, an analog pre-filter, in order to boost high frequency portions of received signals. The analog pre-filter can also provide a direct current (DC) gain if desired. Such communication systems are generally in accordance with 10 gigabit Ethernet standards for transmitting Ethernet frames at a rate of 10 gigabits per second. Examples of such standards established by IEEE 802.3-2008 include, but are not limited to, 10GBASE-KX4, 10GBASE-KR and 10GBASE-T. Such standards generally relate to implementing different 10 Gb physical layer standards that utilize forms of copper as the communication channel. Other standards for interfaces have been developed, such as, for example, XAUI, XFI and 10GBASE-LRM that utilize optical modules and thereby use optical fiber as the communication channel.
With such communication systems, there may be difficulty in selecting an appropriate analog pre-filter. For example, problems can occur when selecting the analog pre-filter according to the amplitude or energy of received signals. In cases where the communication channel consists of a copper wire or traces, channel attenuation is correlated to the length of the wire or trace. However, the degree of frequency dependent loss within the communication channel varies in different cases, i.e., the performance of the communication channel may vary. For example, the analog pre-filter may not function as designed, or the operating parameters, e.g., temperature, may affect the performance of the communication channel. In cases where the communication channel consists of an optical fiber, certain optical to electrical module connections amplify the received signals to a predetermined level for output. In such a case, the signal level of the received signal cannot be used to indicate communication channel quality. In some instances, the analog pre-filter may be selected by “trials.” In other words, the communication system may try various available analog pre-filters and determine if a receiver metric such as, for example, signal to noise ratio (SNR) or bit error rate (BER) meets the desired parameters. However, such trials generally take a long time and increase start-up time for the communication system. Additionally, several choices may work and thus, determining the best analog pre-filter requires an exhaustive search. Also, such trials require decoding of the received signals.